Astrocytes are the major cell type of the central nervous system, wherein they perform a variety of critical roles.- Activities now attributed to these cells include participation in the development and maintenance of neurons and oligodendrocytes, formation of the blood-brain barrier, recycling of glutamate, and potassium homeostasis. Genetic defects in astrocytes have recently been found to cause Alexander disease, a fatal leukodystrophy;and astrocyte dysfunction has also been associated with several other neurological disorders, such as Alzheimer's disease, Down's syndrome and amyotrophic lateral sclerosis (Lou Gehrig's disease). In addition, in response to almost any kind of injury to the brain, astrocytes undergo a change called reactive gliosis, in which they greatly increase the synthesis and release of a large number of molecules. While some of these molecules are thought to ameliorate the injury, others are believed to inhibit repair, including blocking the regeneration of axons. Many fatal brain tumors are also thought to arise from astrocytes. Thus understanding and manipulating the role of astrocytes in the normal and diseased brain is likely of major clinical importance. We are approaching this goal by studying the transcriptional regulation of the gene encoding glial fibrillary acidic protein (GFAP), an astrocyte-specific protein whose synthesis is greatly increased during the reactive response. These studies will primarily be performed by analyzing expression patterns of reporter gene constructs in transgenic mice. In Specific Aim 1 we will perform a detailed analysis of DMA segments that we have previously shown are likely to be important for GFAP gene activity. The objective is to identify the precise DMAsequences required, and then to use this information to isolate and characterize the mediating transcription factors to parse out the signaling pathways involved. In Specific Aim 2 we will develop better tools for expressing transgenes in astrocytes. These tools include GFAP-based promoters that are more specific in their astrocyte specificity, and that are more potent. Relevance to Public Health: The information and tools developed under this proposal will facilitate investigation of the roles of astrocytes in development and disease, and will be used in gene therapy of CNS disorders.